I think that presenting all ex-Warlords in this flashy and super successful way could also be for preparing "the surprise" for Boa's case. Maybe not, but it would be in Oda style.
Also, I don't think that Oda could have the Navy fail on all (and I mean all) fronts: Reverie, Mihawk, Weeble (presumably), Bagy and Boa. A single win is necessary and Boa's capture could cause a major shifting in future events. The fact that at least Koby has been sent there maybe is a hint for the future. Again, maybe not, but he could have been sent to Mihawk, Weeble or Bagy, so why Boa? We have just seen that Oda has no problem in showing us a Warlord destroying a Navy fleet (that for reasons that only Oda knows consisted of pure fodders).
What I am trying to say is that Oda would have had zero problems to draw Boa destroying the Navy's fleet, he did it with Croco and implied it with Mihawk, so Koby's presence would have been useless if he had been there for reaching an agreement or something like that. Also, he didn't let Luffy himself save his own brother back in MF, so now is even less likely that he had let free someone as dangerous as Boa just because she is a friend of Luffy.
So, if I have to bet, I think that "a surprise" with Boa is more likely than not, but maybe I am mistaken: it's more of a guess.